Adaptation in Constitutional Dynamic Libraries and Networks, Switching between Orthogonal Metalloselection and Photoselection Processes

Triply Adaptive Libraries of Dynamic Covalent Macrocycles: Switching between Sorted and Unsorted States

Dynamic noncovalent and covalent chemistries have enabled the constitutional modulation of chemical entities within chemical dynamic systems. The switching between order and disorder, i.e., self-sorted and unsorted states of constitutional dynamic libraries, remains challenging. Herein, we study the adaptive behaviors of a dynamic library of imine macrocycles generated from dialdehydes and diamines, seeking ways to exert control over sorting and unsorting processes. The distribution of constituents in the present library of dynamic macrocycles is modulated in response to internal and external effectors (e.g., time, metal cations, and chemical fuels), resulting in the transient amplification of self-sorted constituents in out-of-equilibrium states. The present study showcases higher complexity in systems subject to multiple adaptation through the dynamic interconversion between singularity/order and diversity/disorder.

Switching between Nonisoenergetic Dynamic Covalent Reactions Using Host-Guest Chemistry

CO2 reacts with simple amines in the presence of water to generate dynamic combinatorial libraries of majority (i.e., ammonium carbamates) and minority (i.e., ammonium carbonates) nonisoenergetic covalent adducts. Over the past two decades, our laboratory has reported on a new class of cavitands, namely, dyn[n]arenes, from which a polyanionic macrocycle is a highly efficient receptor for linear polyammoniums that forms [2]pseudorotaxanes in water at neutral pH. Herein, we demonstrate that the formation of [2]pseudorotaxanes shifts the equilibrium of CO2 capture by polyamines in water toward the quasi-exclusive formation of carbonate adducts, providing the first example of a switch between two competitive and reversible covalent processes triggered by host-guest interactions. In addition, this supramolecular approach to CO2 capture exhibits enhanced capture efficiency by increasing the state of protonation of complexed vs uncomplexed polyamines. Altogether, we report here that a templating approach can divert the outcome of two reversible covalent chemistries involving nucleophilic additions and acid-base reactions, challenging therefore the common knowledge that noncovalent and covalent bonds operate in separate energy frames.

Co(II) Acetate-Assisted Direct Synthesis of Acyl Hydrazones from Acyl Hydrazides under Mild Conditions

Acyl hydrazones are a class of synthetically important organic compounds that are recurrently in high demand for synthesis and use in various fields of chemistry and biology. We report the first Co(II) catalyzed one-component one-pot sustainable synthesis of acyl hydrazones only from acyl hydrazides under mild reaction conditions. Traditional and contemporary methodologies use two components (usually acyl hydrazides and aldehydes/ketones/alcohols/styrene) as the coupling partners. Our protocol, on the other hand, involves the in situ generation of aldehyde intermediate (detected by gas chromatography) from the acyl hydrazide, which then undergoes condensation with another molecule of the same acyl hydrazide in the same pot to yield acyl hydrazones in presence of mild base K2 CO3 and low-cost Co(OAc)2  ⋅ 4H2 O as catalyst. This method shows good functional group tolerance with good to excellent yield of products. Furthermore, some of the resulting acyl hydrazones have been used as synthetic precursors and explored in various post-synthetic modifications to afford N-heterocyclic compounds. Furthermore, photoswitchable properties of few synthesized acyl hydrazones are also explored using their E/Z isomerization around the C=N bond, as realized by high-pressure liquid chromatography (HPLC) and UV-vis spectroscopic studies.

Behavior of a Dynamic Covalent Library Driven by Combined Pd(II) and Biphasic Effectors for Metal Transport between Phases

This work reports the effect of Pd(II) as chemical effector on an acylhydrazone-based dynamic covalent library (DCL) in biphasic systems (water/chloroform). The constituents of the DCL are self-built and distributed in the two phases, two of them are lipophilic enough to play the role of a carrier agent that may transfer Pd(II) from the aqueous phase to the organic phase. Upon addition of Pd(II), the DCL of components exhibits a strong amplification of the constituent that is the most adapted to stabilize Pd(II) in chloroform as well as its agonist in water. This evolution is driven by the combination of the interaction of the DCL with Pd(II) and the presence of the two phases. This study paves the way to a novel approach for liquid/liquid extraction and metal recovery by means of adaptive extractant species generated in situ by a DCL.

New Insights into Acylhydrazones E/Z Isomerization: An Experimental and Theoretical Approach

A family of acylhydrazones have been prepared and characterized with the aim of investigating their potential as information storage systems. Their well-established synthetic methodologies allowed for the preparation of seven chemically stable acylhydrazones in excellent yields that have been photophysically and photochemically characterized. In addition, DFT and TD-DFT calculations have been performed to gain more insights into the structural, energetic and photophysical properties of the E/Z isomers. Our results reveal that E/Z configurational isomerization upon irradiation is highly dependent on the stabilization of the E or Z isomers due to the formation of intramolecular H bonds and the electronic/steric effects intrinsically related to their structures. In addition, Raman spectroscopy is also used to confirm the molecular structural changes after the formation of hydrogen bonds in the isomers.

Photoinduced Crystal-to-Liquid Transition of Acylhydrazone-Based Photoswitching Molecules

A photoinduced crystal-to-liquid transition (PCLT) behavior of new acylhydrazone derivatives (NCs) is reported. The photoswitching of the NCs was identified as a negative photochromism with a high E-to-Z conversion yield (>98%). A kinetic analysis shows a half-life of almost one month. Owing to these high photoswitching performances, we successfully isolated both E- and Z-forms, evaluated their crystal structures, and observed distinct thermal behaviors. The Z-form melts at a lower temperature than the E-form by several tens of degrees. The PCLT occurs at even lower temperatures. UV irradiation induces the E-to-Z conversion in the crystalline state, thereby inducing a eutectic melting. In addition to the PCLT, we observed a photomechanical behavior of the crystals, which suggests that the presented acylhydrazones can be new members of the photoresponsive crystalline materials.

Further Dimensions for Sensing in Biofluids: Distinguishing Bioorganic Analytes by the Salt-Induced Adaptation of a Cucurbit[7]uril-Based Chemosensor

Insufficient binding selectivity of chemosensors often renders biorelevant metabolites indistinguishable by the widely used indicator displacement assay. Array-based chemosensing methods are a common workaround but require additional effort for synthesizing a chemosensor library and setting up a sensing array. Moreover, it can be very challenging to tune the inherent binding preference of macrocyclic systems such as cucurbit[n]urils (CBn) by synthetic means. Using a novel cucurbit[7]uril-dye conjugate that undergoes salt-induced adaptation, we now succeeded in distinguishing 14 bioorganic analytes from each other through the facile stepwise addition of salts. The salt-specific concentration-resolved emission provides additional information about the system at a low synthetic effort. We present a data-driven approach to translate the human-visible curve differences into intuitive pairwise difference measures. Ion mobility experiments combined with density functional theory calculations gave further insights into the binding mechanism and uncovered an unprecedented ternary complex geometry for CB7. TThis work introduces the non-selectively binding, salt-adaptive cucurbit[n]uril system for sensing applications in biofluids such as urine, saliva, and blood serum.

Cagearenes: synthesis, characterization, and application for programmed vapor release

Here, we announce the establishment of a new family of organic molecular cages, named cagearenes, by taking advantage of a versatile strategy. These cagearenes were prepared via the Friedel–Crafts reaction by condensing two equivalents of a precursor bearing three 1,4-dimethoxybenzene groups and three equivalents of formaldehyde. Two cages, namely cagearene-1 and cagearene-2, are obtained and well characterized. The cagearene-1 solid exhibits the ability to adsorb benzene vapour from an equimolar benzene/cyclohexane mixture with a purity of 91.1%. Then, the adsorbed benzene molecules can be released from the cage at a relatively lower temperature, namely 70 °C, as a consequence of which, cyclohexane with a high purity was left within the cage solid. Heating the cage solid further at 130 °C led to the production of cyclohexane with a purity up to 98.7%. As inferred from the single crystal structures and theoretical calculations, the ability of the cage in programmed release of benzene and cyclohexane results from the different binding modes of these two guests.

Two organic cages, cagearene-1 and cagearene-2, are prepared. The cagearene-1 solid selectively absorbs benzene vapor from a benzene/cyclohexane mixture and is used to achieve temperature-controlled programmed vapor release.

Thermodriven, Acidity-Driven, and Photodriven Spin-State Switching in Pyridylacylhydrazoneiron(II) Complexes at or above Room Temperature

The magnetic bistability of spin-crossover (SCO) materials is highly appealing for applications as molecular switches and information storage. However, switching of the spin state around room temperature remains challenging. In this work, we reported the successful manipulation of the spin states of two iron(II) complexes (1-Fe and 2-Fe) based on pyridylacylhydrazone ligands in manifold ways. Both complexes are stabilized in the low-spin (LS) state at room temperature because of the strong ligand-field strength imposed by the ligands. 2-Fe shows thermoinduced SCO above room temperature with a very large and reproducible hysteresis (>50 K), while 1-Fe remains in the LS state up to 400 K. Acidity-driven spin-state switching of the two complexes was achieved at room temperature as a result of the complex dissociation and release of iron(II) in its high-spin (HS) state. Recovery of the complex is feasible upon further alkalization treatment in the case of 1-Fe, allowing bidirectional modulation of the spin state of the metal center. Light-driven one-way switching from LS to HS is also achieved by virtue of E-to-Z isomerization at the C═N double bond, which results in dissociation of the complex because of the poor binding affinity in the Z configuration.

Hydrazones in anion transporters: the detrimental effect of a second binding site

Synthetic anion transporters can be developed using anion receptors that are able to bind the anion and stabilize it in the lipophilic interior of a bilayer membrane, and they usually contain functional groups with acidic NHs, such as ureas, thioureas and squaramides. To assess the suitability of acylhydrazones as a new functional group for the preparation of anion transporters, we have studied a family of thioureas functionalized with these and related functional groups. ¹H NMR titrations and DFT calculations indicate that the thioureas bearing acylhydrazone groups behave as chloride receptors with two separate binding sites, of which the acylhydrazone binds weaker than the thiourea. Chloride transport studies show that the additional binding site has a detrimental effect on thiourea-based transporters, and this phenomenon is also observed for bis(thio)ureas with two separate binding sites. We propose that the presence of a second anion binding unit hinders the transport activity of the thiourea due to additional interactions with the phospholipids of the membrane. In agreement with this hypothesis, extensive molecular dynamics simulations suggest that the molecules will tend to be positioned in the water/lipid interface, driven by the interaction of the NHs of the thiourea and of the acylhydrazone groups with the POPC polar head groups and water molecules. Moreover, the interaction energies show that the poorest transporters have indeed the strongest interactions with the membrane phospholipids, inhibiting chloride transport. This detrimental effect of additional functional groups on transport activity should be considered when designing new ion transporters, unless these groups cooperatively promote anion recognition and transmembrane transport.

Nanoscale Metal-Organic Frameworks: Recent developments in synthesis, modifications and bioimaging applications

Porous Metal-Organic Frameworks (MOFs) have emerged as eye-catching materials in recent years. They are widely used in numerous fields of chemistry thanks to their desirable properties. MOFs have a key role in the development of bioimaging platforms that are hopefully expected to effectually pave the way for accurate and selective detection and diagnosis of abnormalities. Recently, many types of MOFs have been employed for detection of RNA, DNA, enzyme activity and small-biomolecules, as well as for magnetic resonance imaging (MRI) and computed tomography (CT), which are valuable methods for clinical analysis. The optimal performance of the MOF in the bio-imaging field depends on the core structure, synthesis method and modifications processes. In this review, we have attempted to present crucial parameters for designing and achieving an efficient MOF as bioimaging platforms, and provide a roadmap for researchers in this field. Moreover, the influence of modifications/fractionalizations on MOFs performance has been thoroughly discussed and challenging problems have been extensively addressed. Consideration is mainly focused on the principal concepts and applications that have been achieved to modify and synthesize advanced MOFs for future applications.

Accelerated Discovery of α-Cyanodiarylethene Photoswitches

Cyanodiarylethene chromophores are able to undergo constitutional exchange via dynamic covalent chemistry (DCC). During this process, the central ethylene bridge of the molecular scaffold can be broken and thereby enables the assembly of a new combination of aryl moieties around the reformed ethylene bridge. The reversible C═C double bond exchange has exemplarily been investigated using α-cyanostilbenes. Establishing a dynamic equilibrium reaction from α-cyanodiarylethene with arylacetonitriles under mild conditions has been the basis to access constitutional libraries of new photoswitches with potentially improved properties. When subject to irradiation with light of adequate wavelength, α-cyanodiarylethenes undergo Z/E isomerization followed by ring-closure. By screening the thus accessible dynamic chromophore libraries using a desired detection wavelength, we could identify specific dithienyl analogues that exhibit three-state photochromism. The combination of dynamic constitutional libraries of functional chromophores in combination with the light-guided screening and selection should lead to more rapid exploration of structural diversity dye chemistry.

DNA-based constitutional dynamic networks as functional modules for logic gates and computing circuit operations

A nucleic acid-based constitutional dynamic network (CDN) is introduced as a single computational module that, in the presence of different sets of inputs, operates a variety of logic gates including a half adder, 2 : 1 multiplexer and 1 : 2 demultiplexer, a ternary multiplication matrix and a cascaded logic circuit. The CDN-based computational module leads to four logically equivalent outputs for each of the logic operations. Beyond the significance of the four logically equivalent outputs in establishing reliable and robust readout signals of the computational module, each of the outputs may be fanned out, in the presence of different inputs, to a set of different logic circuits. In addition, the ability to intercommunicate constitutional dynamic networks (CDNs) and to construct DNA-based CDNs of higher complexity provides versatile means to design computing circuits of enhanced complexity.

Towards photoswitchable quadruple hydrogen bonds via a reversible "photolocking" strategy for photocontrolled self-assembly

Developing new photoswitchable noncovalent interaction motifs with controllable bonding affinity is crucial for the construction of photoresponsive supramolecular systems and materials. Here we describe a unique "photolocking" strategy for realizing photoswitchable control of quadruple hydrogen-bonding interactions on the basis of modifying the ureidopyrimidinone (UPy) module with an ortho-ester substituted azobenzene unit as the "photo-lock". Upon light irradiation, the obtained Azo-UPy motif is capable of unlocking/locking the partial H-bonding sites of the UPy unit, leading to photoswitching between homo- and heteroquadruple hydrogen-bonded dimers, which has been further applied for the fabrication of novel tunable hydrogen bonded supramolecular systems. This "photolocking" strategy appears to be broadly applicable in the rational design and construction of other H-bonding motifs with sufficiently photoswitchable noncovalent interactions.

Physical organic studies and dynamic covalent chemistry of picolyl heterocyclic amino aminals

A dynamic covalent system of the picolyl heterocyclic amino aminals has been studied. The aminals are characterized as a metastable species and easily switch to other forms via external stimuli. The solvent, temperature, acid-base and substituent effects have been examined to evaluate the dynamic covalent system. The results reveal that a more polar solvent, a lower temperature, basic conditions and an electron-withdrawing moiety contribute to the stabilities of aminals. The existence of the n → π* interaction between acetonitrile and the C[double bond, length as m-dash]N moiety makes the N-pyrimidyl imine (4c and 4d) yield higher in CD3CN. In a similar fashion, all aminals tend to convert to the corresponding hemiaminal ethers in a methanol environment. According to these findings, we successfully synthesized the following species: (a) N-2-picolylpyrimidin-2-amine 6c obtained by reduction using acetonitrile as the specific solvent; (b) a picolyl aromatic amino aminal 3e prepared from 2-pyridinecarboxaldehyde and the electron withdrawing 2-methoxy-5-nitroaniline.

Phase transfer of metal cations by induced dynamic carrier agents: biphasic extraction based on dynamic covalent chemistry

In contrast to the classical method where a single molecule is designed to extract metal cations under specific conditions, dynamic covalent chemistry provides an approach based on the implementation of an adaptive dynamic covalent library for inducing the generation of the extractant species. This approach has been applied to the liquid-liquid extraction of copper(ii) nitrate based on a dynamic library of acylhydrazones constituents that self-build and distribute through the interface of a biphasic system. The addition of copper(ii) cations to this library triggers a modification of its composition and the up-regulation of the ligand molecules driven by coordination to the metal cations. Among these, one species has proven to be sufficiently lipophilic to play the role of carrier agent and its formation by component exchange enables the partial extraction of the copper(ii). The study of different pathways to generate the dynamic covalent library demonstrates the complete reversibility and the adaptability of the system. The detailed analytical investigation of the system provides a means to assess the mechanism of the dynamic extraction process.

Indoline Catalyzed Acylhydrazone/Oxime Condensation under Neutral Aqueous Conditions

Acylhydrazones formation has been widely applied in materials science and biolabeling. However, their sluggish condensation rate under neutral conditions limits its application. Herein, indolines with electron-donating groups are reported as a new catalyst scaffold, which can catalyze acylhydrazone, hydrazone, and oxime formation via an iminium ion intermediate. This new type of catalyst showed up to 15-fold rate enhancement over the traditional aniline-catalyzed reaction at neutral conditions. The identified indoline catalyst was successfully applied in hydrogel formation.

Triple Self-Sorting in Constitutional Dynamic Networks: Parallel Generation of Imine-Based CuI , FeII , and ZnII Complexes

Three imine-based metal complexes, having no overlap in terms of their compositions, have been simultaneously generated from the self-sorting of a constitutional dynamic library (CDL) containing three amines, three aldehydes, and three metal salts. The hierarchical ordering of the stability of the three metal complexes assembled and the leveraging of the antagonistic and agonistic relationships existing between the constituents within the constitutional dynamic network corresponding to the CDL were pivotal in achieving the sorting. Examination of the process by NMR spectroscopy showed that the self-sorting of the FeII and ZnII complexes depended on an interplay between the thermodynamic driving forces and a kinetic trap involved in their assembly. These results also exemplify the concept of "simplexity"-the fact that the output of a self-assembling system may be simplified by increasing its initial compositional complexity-as the two complexes could self-sort only in the presence of the third pair of organic components, those of the CuI complex.

Configurational Selection in Azobenzene-Based Supramolecular Systems Through Dual-Stimuli Processes

Azobenzene is one of the most studied light-controlled molecular switches and it has been incorporated in a large variety of supramolecular systems to control their structural and functional properties. Given the peculiar isomeric distribution at the photoexcited state (PSS), azobenzene derivatives have been used as photoactive framework to build metastable supramolecular systems that are out of the thermodynamic equilibrium. This could be achieved exploiting the peculiar E/Z photoisomerization process that can lead to isomeric ratios that are unreachable in thermal equilibrium conditions. The challenge in the field is to find molecular architectures that, under given external circumstances, lead to a given isomeric ratio in a reversible and predictable manner, ensuring an ultimate control of the configurational distribution and system composition. By reviewing early and recent works in the field, this review aims at describing photoswitchable systems that, containing an azobenzene dye, display a controlled configurational equilibrium by means of a molecular recognition event. Specifically, examples include programmed photoactive molecular architectures binding cations, anions and H-bonded neutral guests. In these systems the non-covalent molecular recognition adds onto the thermal and light stimuli, equipping the supramolecular architecture with an additional external trigger to select the desired configuration composition.

Semiconducting crystalline inorganic-organic hybrid metal halide nanochains

One-dimensional (1D) inorganic-organic metal halide hybrids at the molecular level, which can be considered as arrays of nanochains isolated by organic components, have shown remarkable optical and electric properties. This review summarizes their reported structural types and shows how to modify their band gaps and optical and electric properties.

MicroRNA-Guided Selective Release of Loads from Micro-/Nanocarriers Using Auxiliary Constitutional Dynamic Networks

Two different drug micro-carriers consisting of doxorubicin-dextran (DOX-D)- and camptothecin-modified carboxymethyl cellulose (CPT-CMC)-loaded nucleic acid-stabilized microcapsules, MC-1 and MC-2, or two different nanocarriers consisting of nucleic-acid-locked doxorubicin (DOX)- and camptothecin (CPT)-loaded metal-organic framework nanoparticles, NMOF-1 and NMOF-2, are coupled to auxiliary constitutional dynamic networks, CDNs, for the triggered release of the drugs. CDN "S" composed of four constituents AA'', AB', BA', and BB', and two hairpin structures, H₁ and H₂, leads to the CDN "S"-guided unlocking of the MC-1/MC-2 carriers and the release of DOX-D and CPT-CMC or of the NMOF-1 and NMOF-2 carriers that release DOX and CPT, respectively. The unlocking processes are activated by the cleavage of H₁ and H₂ by BB' and BA', respectively, to yield fragmented strands that unlock the gating units of the microcapsules/NMOFs carriers. In the presence of miRNA-155 or miRNA-124, dictated orthogonal reconfiguration of CDN "S" into CDN "X" or "Y" proceeds. The miRNA-155 stimulates the reconfiguration of CDN "S" to CDN "X", where AA' and BB' are upregulated, and AB' and BA' are downregulated, leading to the enhanced release of DOX-D or DOX from the microcapsule/NMOFs carriers, and to the concomitant inhibition of the release of CPT-CMC or CPT from the respective carriers. Similarly, the miRNA-124-triggered reconfiguration of CDN "S" to CDN "Y" results in the BA'-guided cleavage of H₂ and the preferred release of CPT-CMC or CPT from the respective carriers. The miRNA-triggered CDN-driven unlocking of the carriers stimulates the amplified and selective release of the drugs from the microcapsules/NMOFs carriers.

Self-sorting of two imine-based metal complexes: balancing kinetics and thermodynamics in constitutional dynamic networks

A major hurdle in the development of complex constitutional dynamic networks (CDNs) is the lack of strategies to simultaneously control the output of two (or more) interconnected dynamic processes over several species, namely reversible covalent imine bond formation and dynamic metal–ligand coordination. We have studied in detail the self-sorting process of 11 constitutional dynamic libraries containing two different amines, aldehydes and metal salts into two imine-based metal complexes, having no overlap in terms of their compositions. This study allowed us to determine the factors influencing the fidelity of this process (concentration, electronic and steric parameters of the organic components, and nature of the metal cations). In all 11 systems, the outcome of the process was primarily determined by the ability of the octahedral metal ion to select its pair of components from the initial pool of components, with the composition of the weaker tetrahedral complex being imposed by the components rejected by the octahedral metal ions. Different octahedral metal ions required different levels of precision in the “assembling instructions” provided by the organic components of the CDN to guide it towards a sorted output. The concentration of the reaction mixture, and the electronic and steric properties of the initial components of the library were all found to influence the lifetime of unwanted metastable intermediates formed during the assembling of the two complexes.

Constitutional dynamic networks have been developed to simultaneously control the output of two interconnected dynamic processes over several species of the same reaction mixture.

Stiffness-switchable DNA-based constitutional dynamic network hydrogels for self-healing and matrix-guided controlled chemical processes

Constitutional dynamic networks (CDNs) attract interest as signal-triggered reconfigurable systems mimicking natural networks. The application of CDNs to control material properties is, however, a major challenge. Here we report on the design of a CDN consisting of four toehold-modified constituents, two of which act as bidentate units for chain-elongating, while the other two form a tetradentate structure acting as a crosslinking unit. Their hybridization yields a hydrogel of medium stiffness controlled by the balance between bidentate and tetradentate units. Stabilization of the tetradentate constituent by an auxiliary effector up-regulates the crosslinking unit, yielding a high-stiffness hydrogel. Conversely, stabilization of one of the bidentate constituents by an orthogonal effector enriches the chain-elongation units leading to a low-stiffness hydrogel. Using appropriate counter effectors, the hydrogels are reversibly switched across low-, medium- and high-stiffness states. The hydrogels are used to develop self-healing and controlled drug-release matrices and functional materials for operating biocatalytic cascades.

Dynamic hydrogels with controllable properties are of interest for a range of applications. Here, the authors report on a DNA hydrogel system which can be tailored to have reversible mechanical changes, reversible shape changes, is self-healing and can be used for controlled release applications.

Temperature-controlled repeatable scrambling and induced-sorting of building blocks between cubic assemblies

Separation of a homogeneous mixture of different components to reach an ordered out-of-equilibrium state in solution has attracted continuous attention. While this can be achieved using external chemical fuels or photo energy, an alternative energy source is heat. Here we realize a temperature-controlled cycle of transitions between ordered and disordered states based on a mixture of two kinds of building blocks that self-assemble into cubic structures (nanocubes). An almost statistical mixture of nanocubes (disordered state) is thermodynamically most stable at lower temperature (25 °C), while homoleptic assemblies composed of single components are preferentially produced at higher temperature (100 °C) followed by rapid cooling. The scrambling of the building blocks between the nanocubes takes place through the exchange of free building blocks dissociated from the nanocubes. Based on this mechanism, it is possible to accelerate, retard, and perfectly block the scrambling by the guest molecules encapsulated in the nanocubes.

In this paper, the authors study the temperature-controlled dynamic behavior of a system of nanocubes self-assembled from two different building blocks. Non-intuitively, the disordered, equilibrium state (a mixture of heteroleptic cubes) and the ordered, out-of-equilibrium state (a mixture of homoleptic cubes) are cycled by heating and subsequent rapid cooling.

New Acylhydrazone Photoswitches with Quantitative Conversion and High Quantum Yield but without Hydrogen Bond Stabilizing ( Z)-Isomer

Hydrazones are recently attracting increasing interest because of their facile synthesis and high addressability, fatigue resistance, and modifiability as molecular switches. However, this new class of switches generally suffers from low conversion from E- to Z-configuration. Here, novel benzoylhydrazones were synthesized by condensation of 2-methoxynaphthaldhyde and benzoylhydrazine. In this hydrazone system, both sides of the imine double bond had large steric hindrance, so that the ( E)-isomer of the benzoylhydrazones was less stable and easily converted into the ( Z)-isomer even without an intramolecular hydrogen bond. Up to 99% conversion efficiency and 89% quantum yield were obtained, in addition to excellent addressability and high fatigue resistance. Outstandingly, the crystal structure of one ( Z)-isomer disclosed no intermolecular hydrogen bonds between the molecules of the ( Z)-isomer but strong and sequential hydrogen bonds between those of the ( E)-isomer. Therefore, the ( E)-isomer was less soluble in solvents than the ( Z)-isomer. This molecular switch system could be easily modified by both hydrophilic pentaethylene glycol chains and hydrophobic octyl chains. Under light irradiation, the resultant amphiphilic acylhydrazone could be transferred from ( E)-isomer to ( Z)-isomer in more than 90% yield even in water after light irradiation. Meanwhile, the self-assembled big nanospheres could rearrange into much smaller vesicles because of the solubility difference of ( Z)- and ( E)-isomers. After the anticancer drug procarbazine was loaded by this kind of acylhydrazone in water, it could be released by light irradiation, showing potential application in photocontrollable drug release.

Probing the Dynamics of the Imine-Based Pentafoil Knot and Pentameric Circular Helicate Assembly

We investigate the self-assembly dynamics of an imine-based pentafoil knot and related pentameric circular helicates, each derived from a common bis(formylpyridine)bipyridyl building block, iron(II) chloride, and either monoamines or a diamine. The mixing of circular helicates derived from different amines led to the complete exchange of the N-alkyl residues on the periphery of the metallo-supramolecular scaffolds over 4 days in DMSO at 60 °C. Under similar conditions, deuterium-labeled and nonlabeled building blocks showed full dialdehyde building block exchange over 13 days for open circular helicates but was much slower for the analogous closed-loop pentafoil knot (>60 days). Although both knots and open circular helicates self-assemble under thermodynamic control given sufficiently long reaction times, this is significantly longer than the time taken to afford the maximum product yield (2 days). Highly effective error correction occurs during the synthesis of imine-based pentafoil molecular knots and pentameric circular helicates despite, in practice, the systems not operating under full thermodynamic control.

Consecutive feedback-driven constitutional dynamic networks

Cellular transformations are driven by environmentally triggered complex dynamic networks, which include signal-triggered feedback processes, cascaded reactions, and switchable transformations. We apply the structural and functional information encoded in the sequences of nucleic acids to construct signal-triggered constitutional dynamic networks (CDNs) that mimic the functions of natural networks. Using predesigned hairpin structures as triggers, the network generates functional strands, which stabilize one or the other of the constituents of the network, leading to feedback-driven reconfiguration and time-dependent equilibration of the networks. Using structurally designed hairpins, positive-feedback or negative-feedback mechanisms operated by the CDNs are demonstrated. With two predesigned hairpins, the coupled consecutive operations of negative/positive- or positive/positive- feedback cascades are accomplished. The time-dependent composition changes of the networks are well reproduced by chemical kinetics simulations that provide predictive behaviors of the network, under variable auxiliary conditions. Beyond mimicking natural network properties and functions by means of the synthetic nucleic-acid-based CDNs, the systems introduce versatile perspectives for the design of amplified sensors (sensing of miRNA-376a) and the development of logic gate circuits.

Multiple adaptation of constitutional dynamic networks and information storage in constitutional distributions of acylhydrazones

We report a study of the behavior of four dynamic covalent libraries (DCLs) based on acylhydrazones aAbB and of the corresponding square constitutional dynamic networks (CDNs) NA-ND under the effect of three agents, namely, metal cations, base + metal cations and light irradiation; in particular, the successful switching of the CDN NB between two orthogonal distributions results, respectively, from metallo-selection and photo-selection. The four DCLs undergo triple adaptation when subjected to the three agents with the generation of specific CDN distributions characteristic of each of the four DCLs. The ternary outputs displayed by the DCLs present three states (-1, 0 and 1) related to three different constitutional distributions expressed in response to the triple inputs applied. This latter process amounts to the storage of molecular information in dynamic distributions rather than in selective interactions between complementary entities undergoing molecular recognition.

Light-driven control of the composition of a supramolecular network

The composition of a supramolecular network, constituted by several cucurbituril receptors and guests, can be controlled by the reversible and all-photonic switching of a dithienylethene guest.

Photoswitching hydrazones based on benzoylpyridine

The photoswitching behaviour of three readily accesible benzoylpyridine hydrazones, whose photochromic properties depend on the benzoyl substituent and intermolecular interactions, was investigated.

N-Arylations of trifluoromethylated N-acylhydrazones with diaryliodonium salts as arylation reagents

A novel and efficient N-arylation of trifluoromethylated N-acylhydrazones is described by using diaryliodonium salts as arylation reagents in the presence of copper salts. A wide variety of N-aryl acylhydrazones are obtained with good to excellent yields under mild reaction conditions.

Controlling the Catalytic and Optical Properties of Aggregated Nanoparticles or Semiconductor Quantum Dots Using DNA-Based Constitutional Dynamic Networks

Nucleic acid-based constitutional dynamic networks (CDNs) attract growing interest as a means to mimic complex biological networks. The triggered stabilization of the CDNs allows the dictated guided reversible reconfiguration and re-equilibration of the CDNs to other CDN configurations, where some of the constituents are up-regulated, while other constituents are down-regulated. Although substantial progress in controlling the adaptive dynamic control of the compositions of networks by means of auxiliary triggers was demonstrated, the use of CDNs as active ensembles for controlling chemical functionalities is still a challenge. We report on the assembly of signal-triggered CDN systems that guide the switchable aggregation of Au nanoparticles (NPs), thereby controlling their plasmonic properties and their catalytic functions (Au NPs-catalyzed oxidation of l-DOPA to dopachrome). In addition, we demonstrate that the triggered and orthogonal up-regulation and down-regulation of the constituents of the CDNs leads to the dictated aggregation of different-sized CdSe/ZnS quantum dots (QDs), cross-linked by K⁺-ion-stabilized G-quadruplex units. The incorporation of hemin into the G-quadruplex cross-linking units yields horseradish peroxidase-mimicking DNAzyme units that catalyze the generation of chemiluminescence via the oxidation of luminol by H₂O₂. The resulting chemiluminescence stimulates the chemiluminescence resonance energy transfer (CRET) process to the QDs, resulting in the luminescence of the two-sized QDs. By the application of appropriate triggers, the CDN-dictated up-regulation and down-regulation of the different-sized QDs aggregates are demonstrated, and the control over the photophysical functions of the different-sized QDs, by means of the CDNs, is highlighted.

Exploiting Coupling of Boronic Acids with Triols for a pH-Dependent "Click-Declick" Chemistry

Click-like condensation of boronic acids with specifically designed triols (boronate-triol coupling) produces stable diamantane adducts in aqueous medium, which can be controllably cleaved to initial components under acidic conditions or by using boric acid as a chemical trigger. This novel "click-declick" strategy allows for the creation of temporary covalent connections between two or more modular units, which was demonstrated by the synthesis of new fluorophore-labeled natural molecules (peptides, steroids), supramolecular assemblies, modified polymers, boronic acid scavengers, solid-supported organocatalysts, biodegradable COF-like materials, and dynamic combinatorial libraries.

Crystal structure of aqua-chlorido-(nitrato-κ2O,O')[1-(pyridin-2-yl-κN)-2-(pyridin-2-yl-methyl-idene-κN)hydrazine-κN2]manganase(II)

The search for novel manganese(II) compounds having inter-esting magnetic properties, using 1-(pyridin-2-yl)-2-(pyridin-2-yl-methyl-idene)hydrazine (HL) as a tridendate ligand, led to the preparation of the title mononuclear material, [MnCl(NO3)(C11H10N4)(H2O)], and the determination of its structure by XRD. The asymmetric unit comprises a discrete mol-ecule in which the cation MnII is hepta-coordinated. The environment around the cation is an almost perfect penta-gonal bipyramid. The base is defined by the two N atoms of the pyridine rings, the N atom of the imino function of the ligand and the two O atoms of the chelating bidentate nitrate ligand. The apical positions are occupied by a Cl atom and a water mol-ecule. In the crystal, there are numerous hydrogen bonds of the types Ow-H⋯ONO2 and C-H⋯ONO2, which generate layers parallel to the bc plane in which the ligands in the axial positions point into the inter-layer space. These axial ligands give rise to hydrogen bonds of the types Ow-H⋯ONO2, Ow-H⋯Cl, N-H⋯Cl and C-H⋯Cl, leading to a three-dimensional framework. The chain bridging the two pyridine rings is disordered over two sets of sites in a 0.53 (2):0.47 (2) ratio.